1. Field of the Invention
The present invention relates to methods and burner apparatus for burning fuel gas-air mixtures whereby flue gases having low NOx content are produced.
2. Description of the Prior Art
The environmental emission standards imposed by governmental authorities are continuously becoming more stringent. Such standards limit the quantities of gaseous pollutants such as nitrogen oxides (NOx) and carbon monoxide which can be emitted into the atmosphere. As a result of the standards, improved burner designs have been developed which lower the production of NOx and other polluting gases. For example, methods and apparatus wherein fuel is burned in less than a stoichiometric concentration of oxygen to intentionally produce a reducing environment of carbon monoxide and hydrogen have been proposed. This concept has been utilized in staged air burner apparatus wherein the fuel is burned in a deficiency of air in a first zone producing a reducing environment that suppresses NOx formation and the remaining portion of air is introduced into a second zone.
Methods and apparatus have also been developed wherein all of the air and some of the fuel is burned in a first zone and the remaining fuel is burned in a second zone. In this staged fuel approach, an excess of air in the first zone acts as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NOx. Other methods and apparatus have been developed wherein flue gases are combined with fuel gas-air mixtures to dilute the mixtures and lower their combustion temperatures and the formation of NOx.
While the prior art methods and burner apparatus for producing flue gases having low NOx contents have achieved varying degrees of success, needs still remain for improvement in gas burner apparatus and methods of burning fuel gas whereby simple economical burner apparatus is utilized and lower NOx content flue gases are produced.
The present invention provides improved methods and burner apparatus for burning fuel gas-air mixtures with low NOx formation which meet the above described needs and overcome the deficiencies of the prior art. An improved method of this invention for discharging a mixture of fuel gas and air into a furnace wherein the mixture is burned and flue gases having a low NOx content are formed therefrom is basically comprised of the following steps. A first portion of the fuel gas is mixed with a first portion of the air to form a primary fuel gas-air mixture. The primary fuel gas-air mixture is discharged into a primary burning zone in the furnace from at least one discharge location surrounded by a wall which extends into the furnace. A second portion of the fuel gas and a second portion of the air are mixed to form a secondary fuel gas-air mixture. The secondary fuel gas-air mixture is discharged into a secondary burning zone in the furnace from at least one discharge location adjacent to an exterior side of the wall. The secondary fuel gas-air mixture is discharged at a velocity whereby the mixture is not ignited and burned until after the mixture spreads over the exterior side of the wall, mixes with flue gases in the furnace and flows beyond the wall.
An improved burner apparatus of this invention for discharging a mixture of fuel gas and air into a furnace wherein the mixture is burned and flue gases having low NOx content are formed includes a housing having a forward end which is attached to an opening in the furnace. The forward end of the housing includes a base portion and a wall portion which extends into the furnace. The wall portion surrounds a central area of the base portion. Means are connected to the housing for mixing a first portion of the fuel gas with a first portion of the air to form a primary fuel gas-air mixture and discharging the mixture into a primary burning zone in the furnace from at least one discharge location within the space defined by the central area of the base portion and the interior of the wall portion of the burner housing. Additional means are connected to the housing for mixing a second portion of the fuel gas with a second portion of the air to form a secondary fuel gas-air mixture and discharging the secondary fuel gas-air mixture into a secondary burning zone in the furnace from at least one discharge location adjacent to an exterior side of the wall portion of the burner housing. The secondary fuel gas-air mixture is discharged at a velocity whereby the mixture is not ignited and burned until after the mixture spreads over the exterior side of the wall portion, mixes with flue gases in the furnace and flows beyond the wall portion. In a preferred embodiment, the exterior sides of the wall portion of the housing slant towards the central area of the base portion.
It is, therefore, a general object of the present invention to provide improved methods and burner apparatus for burning fuel with low NOx formation.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.